Simulcast transmission has been employed for years in selective call messaging systems for providing enhanced reliability and improved coverage. Simulcast transmission is accomplished by simultaneously transmitting the same identical signal from two or more geographically separated transmitters. The resultant space diversity is primarily what produces the enhanced reliability and improved coverage.
Good simulcast transmission has always required some form of delay equalization or launch time synchronization to ensure that the transmissions from different transmitters begin at the same time. For low speed data, having the transmissions begin at the same time has usually been sufficient. For the high speed data which is becoming more prevalent today, having the transmissions begin at the same time is necessary, but not sufficient. The reason is that differential transmission delay introduced in the air links can become a significant fraction of the symbol period when the symbol rate is high. When differential transmission delay becomes a significant fraction of the symbol period, intersymbol interference can occur when two or more simulcast signals arrive at the receiver with similar amplitudes. Such intersymbol interference can cause a high error rate in the received signal.
Thus, what is needed is a method and apparatus that can reduce errors caused by intersymbol interference during a simulcast transmission when two or more simulcast signals are received at similar amplitudes with different transmission delays. The method and apparatus preferably will operate without requiring a custom tuning adjustment during installation and system setup.